HIV is the hybrid of two monkey viruses

HIV was born out of a union more than a million years ago between two viruses that infected different species of monkey, a study of the genetic history of HIV-like viruses suggests.

The union took place when chimpanzees preying on the monkeys contracted the viruses, which then combined to form a new type of simian immunodeficiency virus (SIV), the primate version of HIV. It wasn't until the 1930s, though, that this jumped to humans feeding off chimpanzee bush meat in what is now the Democratic Republic of Congo.

SIV in chimps is the precursor to HIV-1, the most widespread form of the human virus. HIV-2, which is restricted to west Africa, is thought to have transferred from sooty mangabeys in Guinea-Bissau in the 1960s.

Until now, it has not been clear where chimp SIV came from, as it contains elements of other SIVs found in different monkey species. But after ...

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